DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 090657
SWODY3
SPC AC 090655

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0155 AM CDT WED MAY 09 2012

VALID 111200Z - 121200Z

...SYNOPSIS...
UPPER-AIR PATTERN IS FCST TO LOSE SOME AMPLITUDE OVER CONUS AS THREE
MAIN PROCESSES OCCUR...
1. E COAST TROUGH FROM DAY-2 MOVES OFFSHORE BY EARLY DAY-3...
2. POSITIVELY TILTED NRN STREAM SHORTWAVE MOVES ENEWD FROM NRN HIGH
PLAINS TO NRN ONT...WHILE CONTINUING GRADUAL DEAMPLIFICATION...AND
3. SRN-STREAM CYCLONE NOW OVER NRN BAJA DRIFTS EWD TO NEWD ACROSS
CENTRAL TX AND CONTINUES SLOW FILLING/WEAKENING.

SFC COLD FRONT RELATED TO CANADIAN-BORDER PERTURBATION WILL MOVE
SEWD ACROSS LS...UPPER MS VALLEY AND CENTRAL PLAINS...REACHING LOWER
MI...IL...MO AND ERN OK BY 12/12Z. THIS FRONT WILL BECOME DIFFUSE
FARTHER W AND SW ACROSS SRN HIGH PLAINS...AMIDST WEAK NLY FLOW ON
BOTH SIDES THAT IS RELATED TO SRN-STREAM SYSTEM. MEANWHILE...GULF
OF MEXICO FRONTAL ZONE DISCUSSED IN DAY-2 OUTLOOK WILL DRIFT NWD
ACROSS PORTIONS S TX AND PERHAPS SWRN LA...WITH WEAK FRONTAL WAVE
LOW OR INFLECTION AREA NEAR TX COAST.

...MIDDLE-UPPER TX COASTAL PLAIN...
TSTMS ARE POSSIBLE INVOF WARM FRONTAL ZONE OVER THIS REGION...WITH
CONDITIONAL THREAT FOR TORNADOES OR DAMAGING GUSTS. ATTM
UNCERTAINTIES ARE TOO GREAT FOR CATEGORICAL RISK AREA.

ALTHOUGH MIDDLE-UPPER LEVEL PERTURBATION WILL BE
WEAKENING...LARGE-SCALE ASCENT AND NRN RIM OF STG UPPER-LEVEL FLOW
WILL SHIFT EWD ACROSS S TX IN ADVANCE OF IT...RELATED TO
CYCLONICALLY CURVED EXIT REGION OF 250-300 MB SUBTROPICAL JET MAX.
MEANWHILE...NEAR-SFC WINDS WILL BE RELATIVELY BACKED INVOF SFC
FRONTAL ZONE...CONTRIBUTING TO ENHANCED DEEP-LAYER SHEAR AND
POTENTIALLY ENLARGED LOW-LEVEL HODOGRAPHS. THOUGH FRONTAL POSITION
VARIES ACROSS S-CENTRAL/SE TX IN PROGS...FCST SOUNDINGS SAMPLING
THAT ENVIRONMENT DEPICT FAVORABLE HELICITY FOR SUPERCELLS AND
POTENTIAL TORNADO THREAT. FURTHER LENDING UNCERTAINTY--DAY-2 TSTM
COMPLEX MAY MODULATE LOCATION/STRENGTH OF FRONTAL ZONE INTO THIS
PERIOD...AND CLOUD COVER/PRECIP FROM EARLIER CONVECTION MAY HINDER
SFC DIABATIC HEATING OVER PARTS OF THIS AREA. WHERE SUSTAINED
HEATING CAN OCCUR...WEAK MIDLEVEL LAPSE RATES WILL BE OFFSET BY RICH
LOW-LEVEL THETAE AND WEAK CINH...TO GENERATE SUFFICIENT BUOYANCY FOR
TSTMS.

...UPPER MS VALLEY REGION...
BAND OF TSTMS MAY DEVELOP ALONG SFC COLD FRONT DURING
AFTERNOON/EARLY EVENING...OVER PORTIONS WI/SERN MN/IA. FCST
SOUNDINGS SUGGEST WEAK DEEP SHEAR...E.G. EFFECTIVE SHEAR LESS THAN
25 KT OVER MOST AREAS...AND MRGL LOW-LEVEL MOISTURE...LIMITING SVR
POTENTIAL.

..EDWARDS.. 05/09/2012

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